Disc drives are data storage devices adapted to store and retrieve user data. A typical disc drive stores data on one or more rotating discs. An actuator positions a corresponding number of data transducing heads (read/write heads) over tracks defined on the rotating discs to access data stored in the tracks.
Generally, track following servo systems are used in hard disc drives to hold the data transducing heads to very small off-track errors in order to support the increasing data density (track density) of contemporary storage devices. Tracking errors can be induced due to many effects including disc and bearing runout, servo-track-writer induced irregularities, electronic noise, spindle and actuator resonances, and external shock and vibration excitations.
Small form factor hard discs are often used in portable computing environments, such as laptop computers, hand-held music players, portable video games, and the like, where there is an increased likelihood of exposure to continuous shocks and random vibrations due to physical activities such as jogging, cycling and the like. Studies of shock and vibration levels in hard disc drives embedded in portable devices during physical activities have shown that shock and vibration levels during jogging can be represented by a continuous series of shock pulses and random vibrations. In portable audio devices, such as MP3 players, which are often used by joggers and cyclists during exercise activities, it is desirable to have a smooth flow of music without interruption. However, external shocks to such portable devices may cause the read-write head in the disc drive to move off track, causing the read-write head to be unable to load information from the storage medium. While such devices often use a memory buffer, the read-write head of the storage device has to recover between shocks in order to continue to read data into the memory buffer, or the system will stop operating.
Shocks induced by jogging typically have a high amplitude and long duration. Traditional servo compensation schemes are not capable of suppressing such disturbances quickly enough to produce satisfactory performance in portable devices. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.